The basic theory and operation of thermoelectric devices has been developed for many years. Presently available thermoelectric devices used for cooling typically include an array of thermocouples which operate in accordance with the Peltier effect. Thermoelectric devices may also be used for heating, power generation and temperature sensing.
Thermoelectric devices may be described as essentially small heat pumps which follow the laws of thermodynamics in the same manner as mechanical heat pumps, refrigerators, or any other apparatus used to transfer heat energy. A principal difference is that thermoelectric devices function with solid state electrical components (thermoelectric elements or thermocouples) as compared to more traditional mechanical/fluid heating and cooling components. The efficiency of a thermoelectric device is generally limited to its associated Carnot cycle efficiency reduced by a factor which is dependent upon the thermoelectric figure of merit (ZT) of materials used in fabrication of the associated thermoelectric elements. Materials used to fabricate other components such as electrical connections, hot plates and cold plates may also affect the overall efficiency of the resulting thermoelectric device.
Thermoelectric materials such as alloys of Bi2Te3, PbTe and BiSb were developed thirty to forty years ago. More recently, semiconductor alloys such as SiGe have been used in the fabrication of thermoelectric devices. Commercially available thermoelectric materials are generally limited to use in a temperature range between 200K and 1300K with a maximum ZT value of approximately one. Typically, a thermoelectric device incorporates both P-type and N-type semiconductor alloys as the thermoelectric materials.
In accordance with one method for the manufacture of a thermoelectric device, a billet of P-type material is extruded to form a P-type extrusion. Similarly, a billet of N-type material is extruded to form an N-type extrusion. The P and N-type extrusions are sliced into wafers, the wafers are sliced into elements, and the elements are mechanically loaded into a grid or “matrix” with the desired pattern and assembled upon a plate. P-type and N-type elements are typically arranged into rectangular arrays, in order to form a thermoelectric device. P-type and N-type legs alternate in both array directions. A metallization may be applied to the P-type wafers, N-type wafers, and/or the plate, in order to arrange the P-type wafers and the N-type wafers electrically in series and thermally in parallel.
For many thermoelectric devices, the elements dimensions are approximately 0.6 mm by 1.0 mm. Generally, the legs have a square cross-section perpendicular to the direction of current flow. Commonly, there are 18 to 36 pairs of P-type and N-type elements. Due to the size of the P-type and N-type elements, the elements are typically separated by hand, by using bowl sorters with pick and place automation, by using mass loading vibratory techniques, or any combination of the three, for installation upon the plate according to a predetermined generally alternating pattern. This method is time-consuming and intricate, and requires specialized equipment and experienced operators.